1. Field of the Invention
The present invention relates to a method for controlling an ultrasonic sensor, and to an ultrasonic sensor.
2. Description of the Related Art
Ultrasonic sensors have been used for decades in vehicles for surrounding-area detection. In this context, the measuring systems are based on an echo method, in which a transmitted signal is reflected by an obstacle and echoed back to the vehicle in the form of an echo signal. The distance of the obstacle from the vehicle is then determined with the aid of the measured echo delay time. This information is then used for many different driver assistance systems, such as parking assistance systems or also blind spot monitoring systems. In this context, the ultrasonic sensors are mostly implemented in the form of an ultrasonic transducer, which allows switching-over between transmit mode and receive mode.
Conventional ultrasonic sensors include a diaphragm, which, in transmit mode, converts mechanical vibrations in the ultrasonic range into pressure fluctuations of the air surrounding the vehicle, and an electromechanical transducer, e.g., in the form of a piezoelectric resonator, which is coupled to the diaphragm, e.g., with the aid of an adhesive bond, and, in transmit mode, converts electrical signals into vibrations in the ultrasonic range. In order to give the radiation of the diaphragm a direction, it is normally mounted to a chassis, which, in contrast to the diaphragm, is supposed to have negligible vibrational amplitudes.
As a rule, ultrasonic sensors are operated in the range of their respective resonant frequency, which results from the resonance characteristics of the respective diaphragm and the respective transducer, since particularly efficient conversion of electrical oscillation power into mechanical vibration power, and vice versa, is present there.
A method for adjusting the resonant frequency of a vibrating section of a housing of an ultrasonic sensor, in which the resonant frequency of the vibrating section is measured and compared to a previously established threshold value of a setpoint resonant frequency, is known from published German patent application document DE 10 2006 021 492 A1. In light of the comparison, the resonant frequency of the vibrating section is adjusted by appropriately removing or applying material.